This bug occurs both with and without split touch controls. When mining/digging (etc) a block, if you move your finger to air before completely breaking it and continue to hold the screen, you will be mining the air.
Another way to do this is to completely break a block in an instance where there is air behind it. If you continue holding the screen after breaking it, you will continue mining air behind it.
This next bug is a result of the above bug. It occurs both with and without split touch controls, but is most noticeable when split touch is enabled. If you transition from mining the air to mining a block, there will be a delay before the block actually begins to be mined. This is even more noticeable when using high resource tools (iron/diamond). The resulting issue is very annoying in that it hinders your mining speed.